Web materials such as printing, industrial and tissue grades of paper, metal foils, cellulose and polymeric films, wires, ropes, strapping and thread are well known. Products made from these web materials are also well known. Ongoing desires to increase the productivity of the manufacturing operations associated with web materials and web products focus at least in part upon increases in the speed of handling of the web materials. As web handling speeds increase, the adverse effects of web material variations on web handling productivity also increase. Dynamic changes in characteristics such as web tensile strength and web modulus of elasticity, may lead to web breaks when the changes are not adequately compensated for in the web-handling process.
The handling of web materials often includes unwinding the material from a roll. The modulus of elasticity of the web material may change over the course of the roll. Changes in the modulus may affect the handling characteristics of the web material. The web material may become more sensitive or less sensitive to changes attempted by the control system of the web-handling process. Sensing changes in the modulus of elasticity as the roll is unwound may enable compensatory changes in the web-handling process to offset the changes in the modulus of elasticity while the web is being handled.
The invention provides a method for the dynamic control of the tension of a moving web material. The web's modulus of elasticity may be used as an input to modify the control scheme of the web-handling process. By sensing changes in the modulus of elasticity, and incorporating the sensed changes into the tension control scheme, the adverse effects of modulus changes may be mitigated.